Commercial and industrial storage tanks are widely used for the bulk storing of liquids. Many of these liquids are highly corrosive and/or are flammable. They pose a significant health and safety hazard if not properly contained. Federal as well as local regulations govern the structure of certain storage tanks.
Heightened public awareness of the danger posed by storage tanks (particularly underground gasoline storage tanks) has led to additional governmental regulations. Recent proposed regulations will soon require most storage tanks to have secondary containment means and possibly a fail safe design feature to guard against accidental soil, water, and air contamination. Secondary containment means must be capable of containing leaked liquid from the storage tank. Rigid double walled tanks made from sheet metal have been suggested as one alternative. While effective for containment purposes, such tanks, as presently available, are costly to build and difficult to install because of their weight. The tanks are built by basically forming two rigid tanks and placing one inside the other.
Tanks made from fiberglass reinforced resinous material are also extensively used. Different methods are used for making these tanks. One commercial method of making tanks from fiberglass reinforced resinous material utilizes a removable split half-mold with shapes for forming the support ribs and end cap along with the main body. After fiberglass and resinous material are applied to the mold and cured, the mold is removed. Next, the interior portions of the rib areas are filled with a filler material or bridged over with a cardboard insert and, fiberglass/resin applied so as to form a substantially smooth tank interior. A second tank half is formed in the same manner and joined with the first tank half. The formed tank is representative of those tanks wherein the support ribs are integrally built into the inner tank as initially made. A double walled tank is made essentially by forming two additional horizontal tank halves, placing the initial single walled tank inside one horizontal half-tank and joining the second horizontal half-tank to the first.
U.S. Pat. No. 4,561,292, contains a description of another method of building a double walled storage tank. As is readily apparent from the patent and above discussion, building a double walled storage tank system with fiberglass and resin by known methods is very labor intensive and costly. Recent concerns about leaked tanks has heightened the need for an efficient and economical manner of building double walled storage tank systems.
There has now been discovered a method whereby storage tanks are built with a double wall for secondary containment in an efficient, yet economical manner. Such tanks can also be equipped with means to monitor for any leakage.